Hydroforming process with the hydrocracking of the products to produce a high octanegasoline



United States Patent 3,192,150 HYDRGFORMING PROCESS WITH THE HYDRO- CRACKING OF THE PRODUCTS T0 PRODUCE A SH OCTANE GASOLINE William F. Taylor, Scotch Plains, and Louis Dauher,

Cranford, N..l., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Julyl, 1963, Ser. No. 291,842 Claims. (Cl. 208-62) The present invention relates to an improvement in hydroforming. More particularly, it relates to an improvement in hydroforming whereby in addition to naphtha reforming, increased amounts of light parafiins, particularly those with branched structures, such as isobutane, isopentane and L.P.G. (liquefied C and C hydrocarbons) are produced. Furthermore, the production of benzene and toluene in relation to heavier aromatics is maximized.

Hydroforming is now a matter of record and commercial practice in this country. Basically, the operation invalves the contacting of a naphtha, either virgin, cracked, Fischer-Tropsch or any mixture thereof, with a solid catalytic material. The contacting takes place at elevated temperatures and pressures in the presence of added hydrogen. However, the process itself produces substantial amounts of hydrogen and in actuality this will almost always surpass the initial hydrogen which has been added to repress deactivation of the catalyst by carbon formation.

The reactions involved in hydroforming are: (1) dehydrogenation of naphthenes to the corresponding aromatic as where methylcyclohexane is dehydrogenated to form toluene, (2) isomerization of paraflins to form branched chain parafi'ins or isomerization of ring compounds, such as ethylcyclopentane to form methylcyclohexane, which latter compound is then dehydrogenated to form toluene, (3) dehydrocyclization of parafiins to are.

'matics such as n-heptane to form toluene, and (4) hydrocracking of the higher boiling constituents of thefeed to form lower boiling constituents.

Hydroforming processes may be divided into two general classes, namely, the semi-regenerative and the cyclic. Inthe latter case, it is possible to use a separate reactor which is, itself, regenerable and may be substituted for any of the other reactors in the circuit while they are being regenerated. This would be obvious to one skilled in the art and, therefore, need not be considered at this time.

In many refinery situations, increased yields of liquefied petroleum gas (L.P.G.), isobutane and isopentane are desirable even at the expense of C yield. This invention discloses a scheme to maximize L.P.G., isobutane, isopentane and lower boiling aromatic yields using a primary reaction zone or zones containing a conventional hydroforming catalyst followed by a secondary reaction zine containing a dehydrogenation activity-free acidic catalyst. The hydroformate from the primary reaction zone is passed through said secondary or catalytic cracking zone to produce the results just enumerated. By a dehydrogenation activity-free catalyst is meant a catalyst having cracking activity but which does not contain any Group VIII transition metal such as platinum, palladium or nickel.

As a result of this treatment a variety of advantages may be realized. The yields of light isoparafiins can be increased beyond that normally obtained in hydroforming.

Of particular importance is the fact that the ratio of the valuable isobutane and isopentane relative to the corresponding normal paraffins is markedly increased. A possible mechanism to explain this improved light isoparafiin yield is that removing the dehydrogenation activity blocks or minimizes the dual-functional isomerization catalytic reaction so that the isoparaflins formed from hydrocracking in much greater than equilibrium proportions do not isomerize to the corresponding normal paraffins. Thus, the ratio of isobutane and isopentane to their corresponding normal paraffins can exceed equilibrium. However, this invention is not contingent on the validity of this mechanism.

Furthermore, the use of a solid, acidic catalyst such as silica-alumina in the secondary reaction zone will re sult in a disproportionately higher benzene and toluene content in the hydroformer effluent.

The increased lower boiling aromatic and isopentane content will result in a gasoline of improvedoverall research octane number and front end volatility. Furthermore, isopentane and benzene are particularly valuable in that they greatly improve the octane number of the lower boiling components of gasoline. This improved front end volatility coupled with the improved octane number of the lower boiling gasoline components is particularly significant in modern times for improving the road performance of low horsepower foreign designed cars which represent an increasing proportion of the car population.

Numerous areas in which L.P.G. plays an important role have sprung into prominence. Included among them is the whole area of alkylation. Isobutane is a valuable feed component for an alkylation plant and the production of this product is substantially increased by this invention.

Recent strides have also been made in the polymerization field, particularly in the production of polypropylene for plastics and 1,3-butadiene for rubber production. Propane and butane serve as the building blocks for these products.

Certain regions of the United States rely on town gas to heat homes and factories. Propane serves as an additive for this gas and greatly improves its heating value.

The accompanying drawing diagrammatically illustrates a preferred embdiment of this invention. Many other modifications will be obvious to one skilled in the art and are intended to be within the scope of the invention.

Turning to the drawing, a desulfurized naphtha is introduced into absorber-debutanizer 11 through line 10. Powerformer off-gas is removed through line 12; this consists mainly of hydrogen, hydrogen sulfide, water and C2". Propane and butane are removed through line 13. The remaining product, boiling in the range of -450 F., is introduced into a series of hydroforming reactors through line 14. There are a series of three hydroformers, 15, 16 and 17, which constitute the primary reaction zone. Each of them contains a suitable hydroforming catalyst. Catalysts that may be used for hydroforming the feed are those containing-0014.0 wt. percent platinum or 0.1-2.0 Wt. percent palladium dispersed upon a highly pure alumina support such as is obtained from aluminum alcoholate, as per US. Patent No. 2,636,865 or from an alumina hydrosol prepared by hydrolyzing aluminum metal with dilute acetic acid in the presence of a very small catalytic amount of mercury. A suitable catalyst comprises about 0.2-0.8 wt. percent platinum widely dispersed upon alumina in the eta or gamma phase derived from a suitable aluminum alcoholate and having a surface area of about 50-300 square meters/gram.

Pressure in the three hydroformers, constituting the primary reaction zone, 15, 16 and 17 should be maintained at about 2005600 p.s.i.g. The feed is preheated to about 850-1000 F. in furnace 18 and is then passed to hydroformer 15 through line 15a. Within hydroformer 15 there is some cooling due to the reaction. Consequently, after the feed is removed from the hydroformer Within hydroformer 16 the feed is once again cooled somewhat by the reaction and, therefore, upon being removed from hydroformer 16 through line 20a it is introduced to furnace 20 where it is once again heated to a temperature of about 850-1000 F. Finally, the feed passes through line 17a into hydroformer 17. ,Temperatures within the hydroformer catalyst bed vary from about 800-1000 F. Hydrogen or hydrogen-rich process or recycle gas is added to the powerformer feed through line 21.

I ..The hydrogen-rich or recycle gas normally contains about 65-90 mol. percent hydrogen with the remainder being light hydrocarbon gases. The exact composition of the recycle gas dependsupon the hydroforming reaction conditions and upon the pressure and temperature at which the recycle gas is separated from the hydroformate. The amount. of recycle gas employed may vary from 500-900 s.c.f./b. and is preferably about 3000-7000 standard cubic feet/barrel of naphtha feed. Under the reaction conditions maintained in hydroformers 15, 16 and 17 there is a tendency for carbon to form on the catalyst and it therefore becomes necessary to regenerate the catalyst. In order to do this and keep the unit in operation a swing reactor (not shown) is provided. The reactor is so manifolded that it may replace any other reactor. In this manner, hydroformers 15,. 16 or 17 may be regenerated with no stoppage of operation. Placing this swing reactor would be obvious to .one skilled in the art and need not be discussed at this time;

The catalyst is regenerated by burning the carbonaceous deposits from the catalyst. Regeneration is preferably effected with diluted air to facilitate control of the temperature ofregeneration. It is preferred to contact the regenerated or carbon-free catalyst with undiluted air or oxygen-enriched gas at temperatures of about 850-1100 F. for from about 1-4 hours. It is also desirable to provide means for subjecting the regenerated catalyst or a portion of it in continuous operation to reactivation with a halogen or halogen compound such as chlorine or hydrogen chloride. A free halogen such as chlorine is the preferred treating agent for reactivation.

Aside fromthe accumulation of poisons the deactivation of hydroforming catalysts proceeds by two mechanisms: (1) the. loss of chlorine or other halogen which is normally'presentas part of the catalyst composition and that contributes substantially to the catalyst activity and. (2) the agglomeration 'of the platinum metal into relatively large or massive crystals having diameters in excess of about 50A. units. Treatment of the catalyst'with a halogen compound such as hydrogen chloride or the'like is effective in restoring halogen content ofthe catalyst to the desired level and to this extent it is efiective in restoring the activity of deactivated or partially deactivated catalyst. On the other hand, treatment of the catalyst with an elementary halogen, such as chlorine or the like, not only restores the catalyst halogen content to the desired level but also accomplishes the redispersion of the platinum metal by breaking up the large platinum'crystallites. v

Regeneration of the catalyst is effected as required by burning carbonaceous materials therefrom with oxygencontaining gas at temperatures of 800-1200 F., pref.- erably at 900-1100 F. The pressure in the regeneration operation may be the same as during, hydroforming or it may, if desired, be lowered to near atmospheric pressure. In burningoif the carbonaceous deposits, at certain amount. of water is formed by combustion of hydrogen in. said deposits, This'water is stripped from the catalyst-and passes overheadrwith the flue gases and is removed from the system. Excess air is used for the regeneration to insure the complete removal of carbon or coke from the catalyst and'to effect reactivation in admixture with chlorine.v The regenerated or carbon free catalyst can advantageously be treated with air at temperatures of 8501100 F. for from about 1-4 hours. The regenerated catalyst is then contacted with chlorine gas or a mixture of chlorine gas and air in order to reactivate the catalyst, restore its chlorine content, and redisperse or break up the large platinum crystallites that formed during the use of the catalyst.

The chlorine partial pressure during reactivation may be in the range of from 0.001-2 atmospheres, preferably, 0.01-1 atmosphere; The quantityof chlorine supplied may be in the range of 0.1-2.0 wt. percent, preferably about 0.5 wt. percent based on the catalyst. The chlorine treatment may be carried out forperiods offrom about 15 seconds to 1 hour,-preferably about 1-15 minutes. While the chlorine-treated catalyst may be subjected to air-stripping to remove excess chlorine, it is usually preferred to avoid. stripping chlorine from the reactivated catalyst since the chlorine content governs. the hydrocracking activity of the catalyst which in turn controls the volatility of the hydroformate.

The amount of chlorine which is desirable to have remaining on the stripped catalyst is related ,to the platinum content of the catalyst. With high platinumcontent catalysts a relatively high chlorine content is desirable and a correspondingly-lower chlorine content is desirable for lower platinum contents. In general, the total amount of chlorine (i.e., both chemically combined and adsorbed) remaining on the catalyst, when employing a catalyst of 0.6 wt. percent platinum content, may be in the range of about.0.2-1.25 Wt. percent and is preferably about 0.5-1.0 wt. percent.

The efiiuent from the primary reaction zone is removed from hydroformer reactor 17 through line 23 and heat exchanger 23a, valve 30a, and is introduced into the secondary reaction zone, reactor 24. This reactor may contain any one of a great variety of fixed bed solid catalysts which are dehydrogenation activity-free and are of the acidic type. Among those which are applicable are those produced by the Filtr'ol Corp. and are known .as Filtrol 58 SR and Catalyst 11. Furthermore, catalysts which are composed of mixtures of alumina and silica, as well as silica and magnesia are applicable. Within this group of catalysts is the catalyst comprising about 13% aluminaand 87% silica. Cracking catalysts made of silica and alumina and containing up to 30% alumina may be used. Other cracking catalysts such as used in catalytic cracking of oils also may be used.

Temperatures within the secondary reaction zone 24 are between 700 and 1100 F. and preferably would be near the temperature of the efiluent from the primary reaction zone since this eliminates the need for large scale heating or cooling between the two zones.

The pressure in the secondary reaction zone is nominally the same as in the primary reaction zone. The hydrogen generated in the primary reaction zone together with that contained in 'the recycle gas tend to suppress carbon formation in the secondary reaction zone 24. The secondary reaction zone can be contained in the tail reactor in a cyclic or semiregenerative hydroformer, or the secondary reaction zone could be contained in a separate reactor used in-conjunotion with a hydroformer. For maximum economy available hydroformer regeneration facilities may be used to regenerate the .secondary reaction zone.

Continuous use of the secondary reaction zone 24 may be obtained by providing an alternate secondary reaction zone reactor 24a to be placed in service while regenerating reactor 24 after carbonaceous deposits are built up to an undesirable high level. When regenerating reactor 24, valve 30a must-be closed. The hydroformed feed after passing through heat exchanger 23a would then pass into line 31a. open when alternate cracking catalyst reactor 24a is in use, and closed when-reactor 24a. is being regenerated.

Along line 31a is valve 32a which would The conditions in alternate cracking catalyst reactor 24a are identical to those used in cracking catalyst reactor 24.

Hydrocracked product from alternate reactor 24a is removed through line 25a and passes through valved line 25 into flash drum 26. Alternately, the function of the secondary reaction zone may be obtained by using a fluid bed catalytic cracker.- The secondary reaction zone can be regenerated with an oxygen-containing gas at temperatures between 800-1250 F.

As a result of this treatment in the secondary reaction zone, the hydroformed product is substantially altered. The product removed from secondary reaction zone 24 is considerably different from that which entered the zone. The product contains substantially more L.P.G., isobutane and isopentane and, in addition, the amount of benzene and toluene in the C fraction is higher.

The product from the secondary reaction zone 24 or alternate zone 24a is removed through line 25 and introduced into flash drum 26. Within the flash drum gaseous and liquid products are separated. Gas is separated and goes off overhead through line 27. Much of the gas is hydrogen. Hydrogen-rich gas in the amount of 500-9000 s.c.f./b. is recycled through line 27 and this recycle gas may be passed through line 28a and into driers and a compressor 28 and then be introduced into line 14 through line 21, or the gas may be passed through line 29 into absorber-debutanizer 11 for use as a stripping gas.

The liquid hydrocarbon product is withdrawn from flash drum 26 through line 30 and directed into the back end fractionation group 31. Within the fractionation unit the liquid product is divided into a plurality of streams. The lightest stream of off-gas is removed through line 32. Propane and butane are recovered as a side stream through line 33; this represents about -25 vol. percent of the original feed. The (3 product may be recovered through line 34 and line 34; this represents about 60-90 vol. per-cent of the original feed, depending on the feed stock and octane level of the product.

The C product may be directed through line 34 and line 3511 into depentanizer 35 to separate a C fraction from a (1 fraction. C -lproduct which may go to gasoline or aromatics recovery is removed from depentanizer 35 through line 36, or a part of the C product may be recycled to the secondary reaction zone 24 for further hydrocracking (by means not shown). The C fraction accounts for about 40-85 v-ol. percent of the original feed. The C fraction is removed overhead through line 37; this fraction comprises between 2 and 15 vol. percent of the original feed. The C fraction is passed into superfractionator 38; here the isopentane is removed overhead through line 39. The isopentane is a high octane product and is desirable for gasoline production. The isopentane may be joined with the C product to form a desirable gasoline.

Norm-a1 pentane is removed from depentanizer 35 through line 40. Since this is a low octane product, it may, if desired, be recycled back through line 40 into line 14 and thereby be mixed with the primary reaction zone feed. In this manner a maximum of the desirable isopentane is produced. In fact, about 60-80% of the C fraction is isopentane.

As an alternative, the (3 product in line 35a may be directed through line 46 to a fractionation unit 48. In this manner a separate benzene stream may be recovered as a side stream through line 49 and a toluene stream may be recovered as a side stream through line 50. Materials heavier than benzene and toluene may be removed through line 52 and, if desired, recycledinto line 40 (not shown).

In order to explain the invention more fully and for comparison, the following specific examples are set forth.

Example 1 A 200/ 300 FVT Baton Rouge naphtha feed is utilized; 10,000 barrels/day of this feed are first desulfurized and then introduced into absorber-debutanizer 11; about 4 million cubic feet of ofl-gas are recovered per day through line 12. About 70-80% by volume of this gas is H About 800 barrels/day of propane and butane are recovered through line 13. About 10,000 barrels/day of feed having a boiling range between and 330 F are removed through line 14 and are passed through hydroformers 15, 16 and 17 in series, comprising the primary reaction zone. The inlet temperature of the feed is about 975 F; the temperature within the reactors is about 940 F; pressure within the reactors is about 400 p.s.i.g. The product from the primary reaction zone was then introduced into the secondary reaction zone 24. Within the zone was a silica-alumina cracking catalyst consisting of silica and 13% A1 0 The catalyst is in pilled form and has a 397 m. g. surface area. The secondary reaction zone 24 is maintained at a temperature of about 940 F. and a pressure of about 400 p.s.i.g.

Effluent from the secondary reaction zone 24 is then introduced into flash drum 26. About 70-80% of the gas taken overhead through line 27 is hydrogen. The liquid product is recovered through line 30 and introduced into back end fractionation unit 31.

From the fractionator about 140,000 s.c.f./d. of off-gas containing C and C hydrocarbons and hydrogen are re covered through line 32. About 850 barrels/ day of propane and butane are recovered through line 33. About 7900 barrels/day of C hydroformate are recovered through line 34 and passed into depentanizer 35. Additionally, 7100 barrels/day of 0 hydroformate are recovered through line 36; including 1230 barrels/day of toluene and 200 barrels/day of benzene, about 630 barrels/day of normal petane and isopentane are removed through line 37 and introduced into superfractionator 38. In this manner iso and normal pentane are separated, about 445 barrels/day of isopentane are mixed with the C hydroformate from line 36 to produce gasoline. The remaining n-pentane is recycled through line 40 and combined with the hydroformer feed transported through line 14.

In this manner a gasoline was produced with a CH- yield of 78.9 vol. percent and a research octane of 88.7. This gasoline has exceptionally good front end volatility. This is to say, the lighter boiling components have a high octane rating. Consequently, cars will start more quickly and there will be less of a tendency for knock within the engine.

Example 2 In this example the identical conditions utilized in Example 1 were employed with one exception; the cracking catalyst reactor 24 is removed. That is to say, the hydroformed product is not subjected to a hydrocracking step. Instead, the product is separated into its component streams. About 10,000 barrels/day of 200/300 FVT Baton Rouge naphtha feed are utilized; the feed is first desulfurized and is then introduced into absorber-debutanizer 11; about 4 million cubic feet of off-gas per day are recovered through line 12, about 70-80% of this gas is hydrogen. About 800 barrels/day of propane and butane are recovered through line 13. About 10,000 barrels/ day of feed having a boiling range between 160 and 330 F. are removed through line 14 and then passed through hydroformers 15, 16 and 17 which are in series and comprise the primary reaction zone. The inlet temperature of the feed is about 975 F.; the temperature within the reactors is about 940 F., pressure within the reactors is about 400 p.s.i.g. The product from the primary reaction zone is then introduced into flash drum 26. The liquid product is recovered through line 30 and introduced into back end fractionation unit 31.

From this fractionator about 2.8 million s.c.f./d. of ofi-gas containing C and C hydrocarbons and hydrogen are recovered through line 32. About 270 barrels/ day of propane and butane are recovered through line 33. About 9100 barrels/day of C hydroformate are recovered through line 34 and passed into depentanizer 35. 8800 barrels/ day of C hydroformate are recovered through line 36 including 860 barrels/day of toluene and 50 barrels/ day of benzene; about 260 barrels/ day of normal and isopentane are removed through line 37 and introduced into superfractionation zone 38. In this manner iso and normal pentane are separated, about 175 barrels/day of isopentane are mixed with and directed along with the C hydroformate to form gasoline. The remaining npentane is recycled through line 40 and combined with hydroforrner feed transported through line 114.

In this manner a gasoline was produced witha C yield of 91.5 vol. percent and the C research octane was 82.2.

Thus, the following improvements in Example 1 with respect to Example 2 are to be noted.

The C research octane level was increased by 6.5. Propane was increased by 4.9 wt. percent. Total L.P.G. yield was increased by 8.3 wt. percent, isopentane yield by 2.7 vol. percent, isobutane yield by 3.2 vol. percent, benzene by 1.6 vol. percent and toluene by 3.7 vol. percent.

It is understood that this invention is not limited to the specific examples which have been offered merely as illustrations and that modifications may be made without departing from the spirit of the invention.

What is claimed is:

1. A process for increasing the isopentane and benzene contents of hydroformed gasoline and for producing maximum L.P.G., which comprises introducing a naphtha into a catalytic hydroforming zone maintained under hydroforming conditions, passing the total elfiuent containing hydrogen from said hydroforming zone into a catalytic hydrocracking zone containing a dehydrogenation activityfree acid type cracking catalyst under hydrocracking conditions to produce a hydrocracked product containing a maximum of benzene, isopentane and L.P.G., passing the hydrocracked product to a flash zone to separate hydrogenrich gases from hydrocracked liquid, recycling said gases to said hydroforming zone, fractionating said hydrocracked liquid into separate streams of gas, propane and butane, and C -lhydrocarbons, passingthe C hydrocarbons into a depentanizing zone whereby a hydrocarbon fraction and a C hydrocarbon fraction are separated, passing the said hydroforming zone and adding the said iso C fraction to the (3 fraction to produce a high octane gasoline.

2. The method of claim 1 in which the said cracking catalyst is silica-alumina.

3. The process of claim 1 where the said 0 hydroformate is passed into an aromatics recovery zone whereby separate streams of C benzene, toluene and a heavier fraction are recovered, and said heavier fraction is mixed with the-said hydroformer feed.

4. A process according to claim 1 wherein said hydroforming zone is maintained at a temperature of 800-1000 F. and a pressure of 200-600 p.s.i.g. and said recycle gas rate is from 500-9000 standard cubic feet of hydrogen/ barrel of oil and said hydrocracking zone is maintained at'a temperature of 800-1000" F. and a pressure of 200 600 p.s.i.g.

5. A process for increasing the isopentane and benzene contents of hydroformed gasoline and for producing maximum L.P.G., which comprises introducing a hydroformer feed into a catalytic hydroforming zone to produce a hydroformed product, passing the total hydroforrned product into a catalytic cracking zone containing a dehydrogenation activity-free acid type cracking catalyst whereby a maximum of benzene, isopentane and L.P.G. are produced, recovering a cracked product, removing hydrogenrich recycle gas from said cracked product to separate a liquid cracked product, recycling said gas to said hydroforming zone, fractionating said liquid cracked product to recover separate streams of off-gas, propane and butane and 0 hydrocarbons, passing said C hydrocarbons into a depentanizing zone whereby a Cg-ifraction and a C hydrocarbon fraction-are separated, passing the said C hydrocarbon fraction into a second fractionation zone whereby separate streamsof iso C and normal C hydrocarbons are recovered, recycling said normal C hydrocarbons to said hydroforming zone, adding the said iso C hydrocarbon fraction to the C hydrocarbon'fraction and thereby producing a high octane gasoline.

References Cited by the Examiner UNITED STATES PATENTS 2,380,279 7/48 Welty 208-66 2,908,629 10/59 Thomas 208-66 3,124,523 3/64 Scott 208-62 ALPHONSO D. SULLIVAN, Primary Examiner. 

1. A PROCESS FOR INCREASING THE ISOPENTANE AND BENZENE CONTENTS OF HYDROFORMED GASOLINE AND FOR PRODUCING MAXIMUM L.P.G., WHICH COMPRISES INTRODUCING A NAPHTHA INTO A CATALYTIC HYDROFORMING ZONE MAINTAINED UNDER HYDROFORMING CONDITIONS, PASSING THE TOTAL EFFLUENT CONTAINING HYDROGEN FROM SAID HYDROFORMING ZONE INTO A CATALYTIC HYDROCRACKING ZONE CONTAINING A DEHYDROGENATION ACTIVITYFREE ACID TYPE CRACKING CATALYST UNDER HYROCRACKING CONDITIONS TO PRODUCE A HYDROCRACKED PRODUCT CONTAINING A MAXIMUM OF BENZENE, ISOPENTANE AND L.P.G., PASSING THE HYDROCRACKED PRODUCT TO A FLASH ZONE TO SEPARATE HYDROGENRICH GASES FROM HYDROCRACKED LIQUID, RECYCLING SAID GASES TO SAID HYDROFORMING ZONE, FRACTIONATING SAID HYDROCRACKED LIQUID INTO SEPARATE STREAMS OF GAS, PROPANE AND BUTANE, AND C5+ HYDROCARBONS, PASSING THE C5+HYDROCARBONS INTO A DEPENTANIZING ZONE WHEREBY A C6+ HYDROCARBON FRACTION AND A C5 HYDROCARBON FRACTION ARE SEPARATED, PASSING THE SAID C5 FRACTION INTO A SECOND FRACTIONATION ZONE WHEREBY SEPARATE STREAMS OF ISO C5 AND NORMAL C5 HYDROCARBONS ARE RECOVERED, RECYCLING SAID NORMAL C5 HYDROCARBONS TO SAID HYDROFORMING ZONE AND ADDING THE SAID ISO C5 FRACTION TO THE C6+FRACTION TO PRODUCE A HIGH OCTANE GASOLINE. 